Desert “Unicorns”: The White Lizards of the Salt Basin Dunes
By Andrew Stuart
In the West Texas countryside on a summer day, you’re apt to glimpse one racing across the ground, or basking in the sun. If you’re a “desert rat” yourself, you’re likely to identify with the small creature’s evident love of the heat.
The lesser earless lizard is a common inhabitant of our region – from the Permian Basin to the desert flats. A humble animal – usually brown, less than 5 inches long. But while it may be “ordinary,” it’s also capable of big surprises.
In 2016, biologist Drew Dittmer was hiking the sparkling dunes of the Salt Basin, in Guadalupe Mountains National Park, when he came upon an earless lizard markedly unlike its peers: it was as white as the shifting sands themselves. Dittmer’s find was new – but similarly “bleached” lizards are found in White Sands National Park, in New Mexico.
Together, these white lizards embody evolution-in-action – and illuminate the fundamental processes behind biodiversity.
Dittmer was a new PhD, teaching at Texas Tech. He’d studied reptiles in Australia, and in the Monahans dunes – and when a friend, a park service staffer, told him about the Guadalupe white sands, his interest was piqued. Dittmer knew about New Mexico’s bleached lizards, and he set off to the Salt Basin on a hunch.
“I was like, I just want to go see this,” Dittmer said. “It was just gut suspicion. I went and I took my camera. I found a white common lesser earless lizard almost immediately.”
The Salt Basin dunes are only a fraction the size of New Mexico’s famous white sands – spanning 3 square miles, compared to 275. Yet a form of the earless lizard had evolved to flourish in this tiny ecological niche.
And it happened fast. These dunes, like those in New Mexico, are only a few thousand years old.
“I think a lot of individuals would think a lot these things take tens if not hundreds of thousands if not millions of years to develop,” Dittmer said. “But I think this at least one line of evidence that is contrasting that – some of these behaviors and morphologies could be developing on a faster scale, at least in some examples.”
With grant funding, Dittmer returned to collect earless lizard specimens.
And he sent samples to Erica Bree Rosenblum. The head of a lab at Berkeley, Rosenblum has been studying New Mexico’s white lizards for 20 years. She’d visited the Salt Basin before – but her search for white lizards there – “like trying to find a unicorn,” she said – failed.
“So then, 20 years later, when Drew got in touch and was like, ‘We found a white morph of one of the lizards you study,’ it was super fun,” Rosenblum said, “because now we can test all sorts of things about how evolution works – besides the fact that it’s just a super adorable and awesome lizard. It happens to be my favorite lizard in the world.”
Rosenblum’s genetic analysis is ongoing. But first results prove that the Texas and New Mexico white lizards evolved independently. Their pale color is attributable to a mutation in a gene underlying melanin production – redheaded humans have a mutation in the same gene.
It is, Rosenblum said, evolution “in black-and-white.” It’s not hard to understand how natural selection favors pale lizards here – blending in, they evade predators. But color is just the most obvious variation. The white lizards’ diets and courtship displays are different. The shapes of their heads and legs have changed, to burrow and run across loose sand.
It’s a window into how new species develop.
And, in a world that’s being rapidly changed by our species, it has implications for the future.
“In the light of people thinking about climate change and other contemporary stressors,” Rosenblum said, “and wondering how quickly biodiversity can adapt to changing conditions, this is a fun example – even though it’s over the course of a couple thousands years, not a couple hundred years – of how quickly evolution can happen when there’s a strong pressure.”
When the dunes were added to the park, in 1998, it was for their unique geology. But preserving land often has impacts and implications we can’t foresee, Dittmer said.
“Nobody acquired the Salt Basin Dunes thinking, ‘Ah! There’s a really unique variety of biodiversity that lives here,’” he said. “The fact that somebody could come here and find this lizard is testament that the parks are protecting biodiversity even when they’re not aware they are.”
Nature Notes is supported by the Shield-Ayres Foundation and produced by Marfa Public Radio with the Sibley Nature Center. The program can be heard each Tuesday and Thursday, at 7:45 a.m. and 4:45 p.m., Central time, on KRTS Marfa, 93.5 FM, and KXWT Odessa/Midland, 91.3 FM. This episode was written by Andrew Stuart.